Recently, a type of power converter, called boost-inverting converter, which combines the boost converter function and the inverting converter function together, has been applied in LCD (Liquid Crystal Display) and CCD (Charge Coupled Device) image devices. For further discussion, an exemplary circuit of a conventional inverting converter 100 is shown in FIGS. 1A and 1B. In the inverting converter 100, a switch SW1 is connected between a capacitor Cout and a node 102, a switch SW2 is connected between an input Vin and the node 102, and an inductor L is connected between the node 102 and ground GND. In the first phase, as shown in FIG. 1A, the switch SW1 turns off and the switch SW2 turns on, and therefore an inductor current I flows from the input Vin to ground GND through the switch SW2 and inductor L, by which the inductor L is energized. After switching to the second phase, as shown in FIG. 1B, the switch SW1 turns on and the switch SW2 turns off, and therefore the inductor L releases the energy stored thereof and the inductor current I becomes to flow from the capacitor Cout to ground GND through the switch SW1 and inductor L. As such, the capacitor Cout is discharged and an inverting voltage Vout1 is produced thereon. On the other hand, a conventional boost converter 200 is shown in FIGS. 2A and 2B, in which an inductor L is connected between an input Vin and a node 202, a switch SW1 is connected between the node 202 and a capacitor Cout, and a switch SW2 is connected between the node 202 and ground GND. In the first phase, as shown in FIG. 2A, the switch SW1 turns off and the switch SW2 turns on, such that an inductor current I flows from the input Vin to ground GND through the inductor L and switch SW2 to energize the inductor L. After switching to the second phase, as shown in FIG. 2B, the switch SW1 turns on and the switch SW2 turns off, and therefore the inductor L releases the energy stored thereof and the inductor current I becomes to flow from the input Vin to the capacitor Cout through the inductor L and switch SW1. As a result, the capacitor Cout is charged and a boost voltage Vout2 is produced thereon. By combining the inverting converter 100 and boost converter 200, as shown in FIGS. 3A to 3C, a conventional boost-inverting converter 300 comprises a switch SW1 connected between a capacitor Cout1 and a node 302, a switch SW2 connected between an input Vin and the node 302, an inductor L connected between the node 302 and a node 304, a switch SW3 connected between the node 304 and ground GND, and a switch SW4 connected between the node 304 and a capacitor Cout2. When the boost-inverting converter 300 operates in an inverting mode, as shown in FIG. 3A for the first phase, the switches SW1 and SW4 turn off and the switches SW2 and SW3 turn on, such that the inductor L is energized by an inductor current I flowing from the input Vin to ground GND through the switch SW2, inductor L and switch SW3. Then the boost-inverting converter 300 is switched from the first phase to the second phase as shown in FIG. 3B, the switches SW1 and SW3 turn on and the switches SW2 and SW4 turn off, and therefore the inductor L releases the energy stored thereof and the inductor current I becomes to flow from the capacitor Cout1 to ground GND through the switch SW1, inductor L and switch SW3, by which the capacitor Cout1 is discharged and an inverting voltage Vout1 is produced thereon. If the boost-inverting converter 300 is to be operated in a boost mode, the inductor L is also energized in the first phase shown in FIG. 3A. However, the boost-inverting converter 300 is then switched from the first phase to the third phase as shown in FIG. 3C, by which the switches SW1 and SW3 turn off and the switches SW2 and SW4 turn on, and therefore the inductor L releases the energy stored thereof and the inductor current I becomes to flow from the input Vin to the capacitor C out2 through the switch SW2, inductor L and switch SW4. Therefore, the capacitor Cout2 is charged and a boost voltage Vout2 is produced thereon.
The boost-inverting converter 300 may excellently operate in single mode, either the inverting mode or the boost mode. Nevertheless, it may not be normally operated in a continuous mode, i.e., switched between the inverting mode and boost mode. If it is switched from one mode to another before the inductor L completely releases the energy stored thereof, error operation will occur in the later mode. For this reason, the boost-inverting converter 300 is always operated either in a pure inverting mode or in a pure boost mode, but never a continuous mode. Furthermore, for both the inverting mode and boost mode to be normally operated, the boost-inverting converter 300 is required to allow for a higher peak inductor current than the inverting converter 100 and boost converter 200. To satisfy such requirement, the switches it employs have more difficult device design and are more expensive, and the power loss when it is operated is greater.
Therefore, it is desired a control apparatus and method to operate a boost-inverting converter in a continuous mode and to allow the boost-inverting converter to have a lower peak inductor current.